The present invention relates to a bearing enabling to receive radial load, axial load exerting in both directions, and moment load, which is used to, for example, industrial machines, robots, medical appliances, food machinery, semi-conductor/liquid crystal making apparatus, optical and optoelectronics apparatus.
As those enabling to receive radial load, axial load exerting in both directions, and moment load by means of one bearing, known are a cross roller bearing shown in FIG. 24, a four point-contacting ball bearing shown in FIG. 25, or a three point-contacting ball bearing shown in FIG. 26.
In the cross roller bearing shown in FIG. 24, a rolling element 300 is a roller, and since the rolling elements 300 and bearing rings 100, 200 make line-contacts at two positions, it has a merit of large moment rigidity. In the four point-contacting ball bearing shown in FIG. 25, or in the three point-contacting ball bearing shown in FIG. 26, the rolling element 400 is a ball, and since the rolling element 400 and the bearing rings 100, 200 make point-contacts at four or three positions, those have merits of low torque and smooth working.
However, the cross roller bearing has the merit of large moment rigidity, while in contrast since the rolling element 300 and the bearing ring 100 make the line-contact, it also has disadvantages of large torque and large torque fluctuation.
In the four or three point-contacting ball bearings, as the rolling element 400 is ball, it has a merit of smaller torque than that of the cross roller in the same dimensions, but on the other hand, it also has a disadvantage of small moment rigidity. In case the radial load is superior to the axial load, or in case of receiving pure radial load, as the respective balls 400 make the four or three point-contacts with the bearing rings 100, 200, spin of the ball 400 is large and a small spin wearing performance is not provided. Further, for improving an ordinary spin wearing performance even being a bit, a space of the bearing is determined to be positive, and as a result, the moment rigidity of the bearing is made small.
For settling these problems, excepting large spin of the four point-contacting ball bearing, a new and useful rolling bearing was previously invented (Japanese Patent Laid Open No. 50264/2001), enabling to receive radial load having lower torque, axial load exerting in both directions, and moment load.
Namely, this rolling bearing has a structure as follows. A plurality of rolling elements are incorporated between a pair of bearing rings, and the respective bearing rings have raceway grooves comprising raceway surfaces Alarger in diameter than radius of the rolling element. At least one of the bearing rings is composed of two raceway surfaces, and the rolling element has the outer diameter portion to be a rolling contact surface having curvatures not only in the radial direction normal to the axial direction but also in the axial direction and concurrently has at least one plane. The rolling elements are alternately arranged on the circumference of the raceway surface as crossing with one another, and the outer diameter portions of the rolling elements always contact at the two points in total one by one on the raceway surface of the opposite one-sided bearing ring and on the raceway surface of the other-sided bearing ring. This rolling bearing has the new and useful working effects as follows.
{circle around (1)} As the rolling elements are alternately arranged on the circumference of the raceway surface as crossing with one another between the inner and outer rings, it is possible to receive the radial load, axial load exerting in both directions, and moment load by means of one bearing.
{circle around (2)} As the respective rolling elements always contact at the only two positions with the inner and outer bearing rings, the sliding owing to relatively large spin that had occurred in the conventional four point contact ball bearing or three point contact ball bearing, so that anti-spin wearing property may be heightened.
{circle around (3)} As the space of the bearing may be set to be small or negative if necessary, the high moment rigidity can be realized.
{circle around (4)} As the rolling element and the bearing ring make the point-contact, rolling resistance is low in comparison with a cross roller, so that a low torque can be realized.
So far, the rolling element incorporated in the rolling bearing is carried out with a machining process when making a blank ball of the rolling element so as to form a plane 501 (FIG. 27A). After forming the plane 501 by the machining process, a spheroidizing process for forming a rolling face 502 depends on a ball mass-production method (for example, described in Japanese Patent Laid Open No. 254858/2000 shown in FIGS. 27B and 27C, spherical balls 500 to be processed (rolling elements) are passed through between mutual grooves of two processing discs 600, 700 opposite with a fixed space so as to turn out substantially spherical balls).
That is, as shown in FIG. 27, the spherical part of the outer diameter portion (or the opposite end face) becoming a rolling face 502 is chucked for processing the plane 501 by means of a grinding tool 800, and therefore, the plane-processing precision is high, but cost for producing the rolling elements is increased, and products are high in comparison with ordinary round balls.
In the conventional machining process, sharp edges 900 are created at a crossing point between the plane 501 and the outer diameter portion 502 (the rolling face) having the curvature. Accordingly, a rounding process is required to the edge 900 after processing the spherical shape of the rolling face 502, and the cost is more heightened.
Under such situations, a unit cost of the rolling element 500 is higher than that of the round ball, and as a result, the cost of the rolling bearing incorporated with this kind of rolling elements 500 is expensive.
Further, it has been found that, also in the proposed rolling bearing (Patent Laid Open No. 50264/2001), the ball as the rolling element has the plane in at least one part of the ball, and always prevents interference between the raceway surface of the opposite one-sided bearing ring and other raceway surface than the raceway surface of the other-sided bearing ring, and at the same time there still remains a room of improving lubricity for avoiding abrasion of the retainer in the contact part (the crossing edge point between the plane of the rolling element and the outer diameter portion having the plane and the curvature) between the rolling element and the retainer.